For a GW event with an electromagnetic counterpart, \(c_{\rm gw}\)  can be constrained by comparison with the arrival time of the photons. For the binary neutron star merger GW170817 and its associated electromagnetic counterpart GRB170817A, the almost coincident observation of both the electromagnetic wave and GW places an exquisite bound on the GW speed [1]}, [2]},
\(-3 \times 10^{-15} \le c_{\rm gw} -1 \le 7\times 10^{-16}.\) 
